Electrode Defined Resonator

ABSTRACT

A bulk acoustic resonator operable in a bulk acoustic mode includes a resonator body mounted to a separate carrier that is not part of the resonator body. The resonator body includes a piezoelectric layer, a device layer, and a top conductive layer on the piezoelectric layer opposite the device layer. A surface of the device layer opposite the piezoelectric layer is for mounting the resonator body to the carrier.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/699,078, filed Jul. 17, 2018, entitled “ElectrodeDefined Resonator”, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a bulk acoustic resonator and, moreparticularly, to a bulk acoustic resonator having a resonator body and,optionally, one or more connecting structures that can be used forsupplying electrical signals to one or more conductive layers of theresonator body.

Description of Related Art

Radio frequency communications have progressed from “1G” system in1980's, to “2G” system in 1990's, “3G” in early 2000's, to current “4G”system that was standardized in 2012. In current RF communications, theRF signal is filtered with surface-acoustic-wave (SAW) filters orbulk-acoustic-wave (BAW) filters.

Film-bulk-acoustic-resonators (FBAR) and Solid-Mounted-Resonators (SMR)are two types of BAW filters that are piezoelectric-drivenmicro-electro-mechanical-system (MEMS) devices that enable current 4G RFcommunications capable of resonating at a relatively high frequency witha relatively low insertion loss, as compared to SAW filter devices.These BAW acoustic resonators comprise a piezoelectric stack thatincludes, in one example, a thin film of piezoelectric materialsandwiched between a thin film top electrode and a thin film bottomelectrode. The resonance frequency of such piezoelectric stack isthickness-based or depends on the thickness of the thin films of thepiezoelectric stack. The resonance frequency increases as the thicknessof thin films of the piezoelectric stack decreases. The film thicknessof the resonant bodies is critical and has to be precisely controlledfor a desirable resonance frequency. It is difficult and time consumingto trim different areas of a piezoelectric stack to achieve a high levelof thickness uniformity for the attainment of a reasonable yield of FBARand SMR fabrication process for a targeted or specified RF frequency.

5G RF communication systems that are being developed will eventuallyreplace the aforementioned lower performance earlier generationcommunication systems that operate at RF frequencies between severalhundreds of MHz and 1.8 GHz. 5G systems will instead operate at RFfrequencies that are much higher, e.g., 3-6 GHz (sub-6 GHz) and possiblyall the way up to 100 GHz, or so.

Because of this increase in frequency, the film thickness for FBAR andSMR-based RF filters for 5G applications would have to be reduced inorder to increase the resonance frequency, which is one of thechallenges current state-of-the-art BAW acoustic resonators face. Thereduction in the piezoelectric film thickness means that the distancebetween top and bottom electrodes of the piezoelectric stack is alsoreduced, which leads to an increase in electric capacitance. Thisincrease in electrical capacitance leads to a higher feedthrough of RFsignal, reducing the signal to noise ratio, which is undesirable. Theoptimal piezoelectric coupling efficiency of a piezoelectric stack(including top electrode, a bottom electrode, and a piezoelectric layersandwiched between the top and bottom electrodes) can result from aproper combination of the thickness of the piezoelectric layer, thethickness of the top electrode, the thickness of the bottom electrode,and the alignment and orientation of the piezoelectric crystal(s). Thereduction in the piezoelectric film thickness for the purpose ofachieving the desirably high RF frequency operation for 5G communicationmay not allow the attainment of an optimal piezoelectric couplingefficiency, which results in a higher insertion loss and a higher motionimpedance. The thickness of the electrodes, either the top electrode,the bottom electrode, or both, may also need to be reduced. Reduction inelectrode thickness leads to an increase in electrical resistivity,which leads to another undesirable limitation, namely, higher insertionloss.

Furthermore, the product of frequency and Quality-Factor (or Q) of FBARand SMR devices are typically constant, which means that an increase inresonance frequency will lead to a decrease in Q. A decrease in Q isundesirable, particularly given that the state of art of FBAR and SMR'sQ is approaching the theoretical limit at a frequency 2.45 GHz or below.Therefore, doubling the frequency will lead to a reduction of Q value,which is not desirable for making a RF devices such as an RF filter, anRF resonator, an RF switch, an RF oscillator, etc.

SUMMARY OF THE INVENTION

Generally, provided is a resonator body that can operate in a bulkacoustic mode, preferentially in a lateral resonance mode. The bottom ofthe resonator body can be mounted or coupled to a mounting substrate orcarrier while still allowing the use of the resonator body as an RFfilter, an RF resonator, an RF switch, an RF oscillator, etc.

Also provided is a bulk acoustic resonator that includes the resonatorbody and one or more connecting structures that enable electricalsignals to be provided to one or more conductive layers of the resonatorbody. In one preferred and non-limiting embodiment or example, the oneor more connecting structures can be integral with and/or formed fromthe same layers of materials as the resonator body whereupon the bulkacoustic resonator can be a unitary piece. The bottom of the unitarypiece bulk acoustic resonator can be mounted or coupled to a mountingsubstrate or carrier while still allowing the use of the resonator bodyas an RF filter, an RF resonator, an RF switch, an RF oscillator, etc.

BRIEF DESCRIPTION OF THE DRAWING(S)

These and other features of the present invention will become moreapparent from the following description in which reference is made tothe appended drawings wherein:

FIG. 1 is a side view of one preferred and non-limiting embodiment orexample unsuspended bulk acoustic resonator according to the principlesof the present invention;

FIG. 2 is a side view of one preferred and non-limiting embodiment orexample unsuspended bulk acoustic resonator according to the principlesof the present invention;

FIG. 3 is a side view of one preferred and non-limiting embodiment orexample unsuspended bulk acoustic resonator according to the principlesof the present invention;

FIG. 4A is an isolated plan view of one preferred and non-limitingembodiment or example form of an interdigitated electrode that can beused as a top conductive layer, an optional bottom conductive layer, orboth of an unsuspended bulk acoustic resonator according to theprinciples of the present invention;

FIG. 4B is an isolated plan view of one preferred and non-limitingembodiment or example form of a comb electrode that can be used as a topconductive layer, an optional bottom conductive layer, or both of anunsuspended bulk acoustic resonator according to the principles of thepresent invention;

FIG. 4C is an isolated plan view of one preferred and non-limitingembodiment or example form of a sheet electrode that can be used as atop conductive layer, an optional bottom conductive layer, or both of anunsuspended bulk acoustic resonator according to the principles of thepresent invention;

FIGS. 5A-5B are sections of preferred and non-limiting embodiments orexamples taken along lines A-A and B-B in each of FIGS. 1-3;

FIGS. 6A-6B are sections of preferred and non-limiting embodiments orexamples taken along lines A-A and B-B in each of FIGS. 1-3;

FIGS. 7A-7B are sections of preferred and non-limiting embodiments orexamples taken along lines A-A and B-B in each of FIGS. 1-3;

FIG. 7C is a side view of one preferred and non-limiting embodiment orexample unsuspended bulk acoustic resonator according to the principlesof the present invention with materials of the first and secondconnecting structures and on both sides of the tether conductors removedas shown in FIGS. 7A-7B;

FIGS. 8A-8B are sections of preferred and non-limiting embodiments orexamples taken along lines A-A and B-B in each of FIGS. 1-3;

FIG. 8C is a side view of one preferred and non-limiting embodiment orexample unsuspended bulk acoustic resonator according to the principlesof the present invention with materials of the first and secondconnecting structures and on both sides of the tether conductors removedas shown in FIGS. 8A-8B;

FIG. 8D is a side view of one preferred and non-limiting embodiment orexample unsuspended bulk acoustic resonator according to the principlesof the present invention with materials of the first and secondconnecting structures and on both sides of the tether conductors removedas shown in FIGS. 8A-8B;

FIGS. 9A-9B are sections of preferred and non-limiting embodiments orexamples taken along lines A-A and B-B in each of FIGS. 1-3;

FIG. 9C is a side view of one preferred and non-limiting embodiment orexample unsuspended bulk acoustic resonator according to the principlesof the present invention with materials of the first and secondconnecting structures and on both sides of the tether conductors removedas shown in FIGS. 9A-9B;

FIG. 9D is a side view of one preferred and non-limiting embodiment orexample unsuspended bulk acoustic resonator according to the principlesof the present invention with materials of the first and secondconnecting structures and on both sides of the tether conductors removedas shown in FIGS. 9A-9B; and

FIG. 10 is a plot of frequency vs. dB for a resonator body having abottom conductive layer in the form of a sheet electrode and a topconductive layer in the form of an comb electrode with a finger pitch of1.8 μm.

DESCRIPTION OF THE INVENTION

For the purposes of the following detailed description, it is to beunderstood that the invention may assume various alternative variationsand step sequences, except where expressly specified to the contrary. Itis also to be understood that the specific devices and methods describedin the following specification are simply exemplary embodiments,examples, or aspects of the invention. Moreover, other than in anyoperating examples, or where otherwise indicated, all numbersexpressing, in preferred and non-limiting embodiments, examples, oraspects, quantities of ingredients used in the specification and claimsare to be understood as being modified in all instances by the term“about”. Accordingly, unless indicated to the contrary, the numericalparameters set forth in the following specification and attached claimsare approximations that may vary depending upon the desired propertiesto be obtained by the present invention. Accordingly, each numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

It is also to be understood that the specific devices and processesillustrated in the attached drawings, and described in the followingspecification, are simply exemplary embodiments, examples, or aspects ofthe invention. Hence, specific dimensions and other physicalcharacteristics related to the embodiments, examples, or aspectsdisclosed herein are not to be considered as limiting. Certain preferredand non-limiting embodiments, examples, or aspects of the presentinvention will be described with reference to the accompanying figureswhere like reference numbers correspond to like or functionallyequivalent elements.

In this application, the use of the singular can include the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances. Further, in this application, the use of “a”or “an” means “at least one” unless specifically stated otherwise.

For purposes of the description hereinafter, the terms “end,” “upper,”“lower,” “right,” “left,” “vertical,” “horizontal,” “top,” “bottom,”“lateral,” “longitudinal,” and derivatives thereof shall relate to theexample(s) as oriented in the drawing figures. However, it is to beunderstood that the example(s) may assume various alternative variationsand step sequences, except where expressly specified to the contrary. Itis also to be understood that the specific example(s) illustrated in theattached drawings, and described in the following specification, aresimply exemplary examples or aspects of the invention. Hence, thespecific examples or aspects disclosed herein are not to be construed aslimiting.

With reference to FIG. 1, in one preferred and non-limiting embodimentor example, an unsuspended bulk acoustic resonator (UBAR) 2 inaccordance with the principles of the present invention, that can beoperable in a bulk acoustic mode, can include a resonator body 4 thatcan include from a top thereof to a bottom thereof a stack of layerscomprising a top conductive layer 6, a piezoelectric layers 8, anoptional bottom conductive layer 10, and a device layer 12. In theexample UBAR 2 shown in FIG. 1, the bottom of device layer 12 can bemounted, e.g., mounted directly, to a mounting substrate or carrier 14.

With reference to FIG. 2 and with continuing reference to FIG. 1, in onepreferred and non-limiting embodiment or example, another example UBAR 2in accordance with the principles of the present invention can besimilar to UBAR 2 shown in FIG. 1 with at least the exception thatresonator body 4 in FIG. 2 can include an optional substrate 16 betweendevice layer 12 and carrier 14. In an example, the bottom of devicelayer 12 can be mounted, e.g., mounted directly, to the top of substrate16 and the bottom of substrate 16 can be mounted, e.g., mounteddirectly, to carrier 14.

With reference to FIG. 3 and continuing reference to FIGS. 1 and 2, inone preferred and non-limiting embodiment or example, another exampleUBAR 2 in accordance with the principles of the present invention can besimilar to UBAR 2 shown in FIG. 2 with at least the exception thatresonator body 4 in FIG. 3 can include an optional second substrate 16-1between device layer 12 and piezoelectric layer 8 or optional bottomconductive layer 10, if provided, and/or an optional second device layer12-1 between second substrate 16-1 and piezoelectric layer 8 or optionalbottom conductive layer 10, if provided. In one preferred andnon-limiting embodiment or example, it is envisioned that resonator body4 in FIG. 3 can further include one or more additional device layers 12(not specifically shown) and/or one or more additional substrates 16(not specifically shown) as deemed suitable and/or desirable. An exampleresonator body 4 having a number of device layers 12 and substrates 16can include, in an exemplary order from piezoelectric layer 8 oroptional bottom conductive layer 10, if provided, to carrier 14, thefollowing: a first device layer, a first substrate; a second devicelayer, a second substrate; a third device layer, a third substrate; . .. and so forth. In one preferred and non-limiting embodiment or example,where resonator body 4 can include a plurality of device layers 12and/or a plurality of substrates 16, each device layer 12 can be made ofthe same or a different material and each substrate 16 can be made ofthe same or a different material. In one preferred and non-limitingembodiment or example, the number of device layers 12 and the number ofsubstrates 16 can be different. In an example, in an exemplary orderfrom piezoelectric layer 8 or optional bottom conductive layer 10, ifprovided, to carrier 14, resonator body 4 can include the following:device layer 12-1, substrate 16-1, and device layer 12 as the bottommostlayer of resonator body 4. Examples of materials that can be used toform each device layer 12 and each substrate 16 will be describedhereinafter.

In one preferred and non-limiting embodiment or example, as shown inFIGS. 1-3, one or more optional temperature compensation layer 90, 92,and 94 can be provided on the top surface of top conductive layer 6;between piezoelectric layer 8 or optional bottom conductive layer 10, ifprovided, and device layer 12; and/or between device layer 12 (or 12-1)and substrate 16 (or 16-1), if provided. Each temperature compensationlayer can comprise at least one of silicon and oxygen. In an example,each temperature compensation layer can comprise silicon dioxide, or asilicon element, and/or an oxygen element. When provided, the one ormore optional temperature compensation layer 90, 92, and 94 can helpavoid a change in the resonant frequency of each example resonator body4 shown in FIGS. 1-3 due to heat generated during use.

In plan view, each resonator body 4 and/or UBAR 2 described herein canhave a square or rectangular shape. However, resonator body 4 and/orUBAR 2 having other shapes is envisioned.

With reference to FIG. 4A-4C and with continuing reference to allprevious figures, in one preferred and non-limiting embodiment orexample, one or both of conductive layer 6 and optional conductive layer10 can be in the form of an interdigitated electrode 18 (FIG. 4A) thatcan include conductive lines or fingers 20, supported by a back 22,interdigitated with conductive lines or fingers 24, supported by a back26. In one preferred and non-limiting embodiment or example, one or bothof conductive layer 6 and optional conductive layer 10 can be in a formof a comb electrode 27 (FIG. 4B) that can include conductive lines orfingers 28 extending from a first back 30. The ends of conductive linesor fingers 28 opposite first back 30 can be connected to an optionalsecond back 32 (shown in phantom in FIG. 4B). In one preferred andnon-limiting embodiment or example, one or both of conductive layer 6and optional conductive layer 10 can be in a form of a conductive sheetelectrode 33 (FIG. 4C). Each line or finger 20, 24 and 28 is shown as astraight line. In an example, each line or finger 20, 24 and 28 may bean arched line or finger, a spiral line or finger, or any other suitableand/or desirable shape.

In one preferred and non-limiting embodiment or example, top conductivelayer 6 can be in the form of an interdigitated electrode 18, or a combelectrode 27, or a sheet electrode 33. Independent of the form of topconductive layer 6, optional bottom conductive layer 10, if provided,can be in the form of an interdigitated electrode 18, or a combelectrode 27, or a sheet electrode 33. Hereinafter, and for the purposeof description only, in one preferred and non-limiting embodiment orexample, top conductive layer 6 will be described as being in the formof a comb electrode 27, that includes the first back 30 and the optionalsecond back 32, and optional bottom conductive layer 10 will bedescribed as being in the form of sheet electrode 33. However, this isnot to be construed in a limiting sense since the use is envisioned ofany one of interdigitated electrode 18, or comb electrode 27, or sheetelectrode 33 for top conductive layer 6, in combination with any one ofinterdigitated electrode 18, or comb electrode 27, or sheet electrode 33for optional bottom conductive layer 10.

In one preferred and non-limiting embodiment or example, the resonantfrequency of each example resonator body 4 having at least topconductive layer 6 in the form of interdigitated electrode 18 or combelectrode 27, regardless of the form of optional bottom conductive layer10, if provided, can be tuned or selected in a manner known in the artby appropriate selection of a finger pitch 38 (see e.g., FIGS. 4A-4B),wherein finger pitch 38=finger width+finger gap (between adjacentfingers). In an example, where it is desired that each example resonatorbody 4 resonate primarily, but not entirely, in lateral mode, versus athickness mode, the resonant frequency of resonator body 4 can beincreased by decreasing the finger pitch 38. In an example, where it isdesired that each example resonator body 4 resonate primarily, but notentirely, in the thickness mode, versus lateral mode, the resonantfrequency of resonator body 4 can be decreased by increasing the fingerpitch 38.

In one preferred and non-limiting embodiment or example, each exampleresonator body 4 can resonate in a thickness mode, a lateral mode, or ahybrid or a composite mode which is the combination of thickness modeand lateral mode. For thickness mode resonance, the acoustic waveresonates in the direction of piezoelectric layer 8 thickness and theresonant frequency is based on the thickness of the piezoelectric layer8, and the thickness of the top conductive layer 6 and the optionalbottom conductive layer 10, if provided. The combination ofpiezoelectric layer 8, optional bottom conductive layer 10, if provided,and top conductive layer 6 may be referred to as a piezoelectric stack.The acoustic velocity that determines the resonant frequency of eachexample resonator body 4 described herein is a composite acousticvelocity of the piezoelectric stack. In an example, the resonantfrequency, f, can be calculated by dividing the composite acousticvelocity, V_(a), by twice the piezoelectric stack thickness, τ.

For lateral mode resonance, the acoustic wave resonates in a lateraldirection (x or y direction) of piezoelectric layer 8 and the resonantfrequency can be determined by dividing the composite acoustic velocityof the piezoelectric stack, V_(a), by twice the finger pitch 38,f=V_(a)/2(finger pitch). When the finger pitch is reduced from a largepitch size, δ_(L), to a small pitch size, δ_(S), the percentage of thefrequency increase, PFI_(Calculated), can, in an example, be determinedby

PFI_(Calculated)=(δ_(L)−δ_(S))/δ_(S)).

In an example, when the finger pitch 38 is reduced from 2.2 μm to 1.8μm, the PFI_(Calculated) for lateral mode is 22.2%. In another example,when the finger pitch 38 is reduced from 1.8 μm to 1.4 μm, thePFI_(Calculated) for a lateral mode is 28.5%.

A composite mode resonance can include a portion of thickness moderesonance and a portion of lateral mode resonance. The portion of thelateral mode resonance, L, in a composite mode resonance can be definedby a ratio of the real or measured percentage of the frequency increase,PFI_(Measured), to a calculated percentage of the frequency increase,PFI_(Calculated), by changing the finger pitch 38 from a large pitchsize, δ_(L), to a small pitch size, δ_(S). The lateral mode resonance,L, value can be greater than 100% if there are one or more uncontrolledor unforeseeable variations. In an example, resonator body 4 canresonate in a thickness mode, in a lateral mode, or in a composite mode.In an example of composite mode resonance, the portion of the lateralmode resonance, L, can be ≥20%. In another example of composite moderesonance, the portion of the lateral mode resonance, L, can be ≥30%. Inanother example of composite mode resonance, the portion of the lateralmode resonance, L, can be ≥40%.

In one preferred and non-limiting embodiment or example, a resonatorbody 4 having optional bottom conductive layer 10 in the form of sheetelectrode 33 and a top conductive layer 6 in the form of comb electrode27 with a finger pitch 38 of 2.2 μm can resonate in composite mode withthe following mode resonant frequencies: Mode1 resonant frequency=1.34GHz; Mode2 resonant frequency=2.03 GHz; and Mode3 resonantfrequency=2.82 GHz.

In an example, for resonator body 4 having optional bottom conductivelayer 10 in the form of sheet electrode 33 and a top conductive layer 6in the form of comb electrode 27 with a finger pitch 38 of 1.8 82 m,resonator body 4 can resonate in composite mode with the following moderesonant frequencies: Mode1 resonant frequency=1.49 GHz; Mode2 resonantfrequency=2.38 GHz; and Mode3 resonant frequency=3.05 GHz. In thisexample, the percentage of lateral mode resonance, L, of the compositemode resonance can be: Lmode1=53%; Lmode2=78%; and Lmode3=27%,respectively. See also FIG. 10 which is a plot of frequency vs. dB forthis example resonator body 4. In FIG. 10, each peak 82, 84 and 86,represents a response of resonator body 4 at the respective Mode1resonant frequency=1.49 GHz; the Mode2 resonant frequency=2.38 GHz; andthe Mode3 resonant frequency=3.05 GHz.

In an example, for resonator body 4 having optional bottom conductivelayer 10 in the form of sheet electrode 33 and a top conductive layer 6in the form of comb electrode 27 with a finger pitch 38 of 1.4 μm,resonator body 4 can have the following mode resonant frequencies: Mode1resonant frequency=1.79 GHz; Mode2 resonant frequency=2.88 GHz; andMode3 resonant frequency=3.36 GHz. For this example resonator body 4,the percentage of lateral mode resonance, L, of the composite moderesonance can be: Lmode1=70%; Lmode2=74%; and Lmode3=35%.

In an example, the foregoing description of resonator body 4 resonatingin a thickness mode, in a lateral mode, or in a composite mode, can alsobe applicable to each example UBAR 2 shown in FIGS. 1-3 that can includea resonator body 4 in combination with one or more connecting structures34 and 36, described in more detail hereinafter.

With ongoing reference to FIGS. 1-3, in one preferred and non-limitingembodiment or example, the bottommost layer of each resonator body 4shown in FIGS. 1-3 can be mounted directly to carrier 14 utilizing anysuitable and/or desirable mounting technique, e.g., eutectic mounting,adhesive, etc. Herein, “mounted directly”, “mounting . . . directly”,and similar phrases are to be understood as the bottommost layer of eachresonator body 4 shown in FIGS. 1-3 being positioned proximate tocarrier 14 and joined to carrier 14 in any suitable and/or desirablemanner, such as, in an example, mounting, attaching, etc., and/or by anysuitable and/or desirable means, such as, in an example, eutecticbonding, conductive adhesive, non-conductive adhesive, etc. In onepreferred and non-limiting embodiment or example, carrier 14 can be asurface of a package, such as an conventional integrated circuit (IC)package. After the bottommost layer of a resonator body 4 is mounted tothe surface of said package, resonator body 4, and, more generally, UBAR2, can, in a manner known in the art, be sealed in said package toprotect resonator body 4, and, more generally, UBAR 2, against externalenvironmental conditions. In an example, the use of a package, like aconventional ceramic IC package commercially available from, e.g., NTKCeramic Co., Ltd. of Japan, for mounting UBAR is envisioned. However,this is not to be construed in a limiting sense since it is envisionedthat resonator body 4 and/or UBAR 2 can be mounted in any suitableand/or desirable package now known or hereinafter developed.

In another example, carrier 14 can be the surface of an substrate, suchas, for example, a sheet of ceramic, a sheet of conventional printedcircuit board material, etc. The description herein of examplesubstrates to which the bottommost layer of each resonator body 4 and/orUBAR 2 shown in FIGS. 1-3 can be mounted is for illustration purposesonly and is not to be construed in a limiting sense. Rather, carrier 14can be made of any suitable and/or desirable material that is notincompatible with the material forming the bottommost layer of eachresonator body 4 and/or UBAR 2 shown in FIGS. 1-3 and which enables theuse of resonator body 4 and/or UBAR 2 in a manner known in the art.Carrier 14 can have any form deemed suitable and/or desirable by oneskilled in the art. Accordingly, any description herein of mountingsubstrate or carrier 14 is not to be construed in a limiting sense.

With ongoing reference to FIGS. 1-3, in one preferred and non-limitingembodiment or example, each UBAR 2 can include one or more optionalconnecting structures 34 and/or 36 that facilitate the application ofelectrical signals to top conductive layer 6 and optional bottomconductive layer 10, if provided, of resonator body 4. In one preferredand non-limiting embodiment or example, however, the one or moreoptional connecting structures 34 and/or 36 may be excluded (i.e., notprovided) where electrical signals can be applied directly to topconductive layer 6 and optional bottom conductive layer 10, if provided,of resonator body 4. Accordingly, in an example, UBAR 2 can compriseresonator body 4 without connecting structures 34 and 36. In anotherexample, UBAR 2 can comprise resonator body 4 and a single connectingstructure 34 or 36. For the purpose of description only, in onepreferred and non-limiting embodiment or example, UBAR 2 comprisingresonator body 4 and connecting structures 34 and 36 will be described.

Each connecting structure 34 and 36 can have any suitable and/ordesirable form, can be formed in any suitable and/or desirable manner,and can be made of any suitable and/or desirable material(s) that canfacilitate the provision of separate electrical signals to topconductive layer 6 and optional bottom conductive layer 10, if provided.In an example, where top conductive layer 6 is in the form of combelectrode 27 with only one back 30 or 32, and optional bottom conductivelayer 10 is in the form of comb electrode 27 with only one back 30 or32, or sheet electrode 33, electrical signals can be provided to each oftop conductive layer 6 and optional bottom conductive layer 10 via asingle connecting structure 34 or 36 that can be configured to provideseparate electrical signals to top conductive layer 6 and optionalbottom conductive layer 10.

In another example, where at least one of top conductive layer 6 oroptional bottom conductive layer 10 has the form of interdigitatedelectrode 18 or comb electrode 27 having two backs 30 and 32, separateconnecting structures 34 and 36 can be provided to separately provideone or more electrical signals to backs 24 and 26 of interdigitatedelectrode 18 and/or to backs 30 and 32 of comb electrode 27. The formsof top conductive layer 6 and optional bottom conductive layer 10 andmanner in which electrical signals are provided to top conductive layer6 and optional bottom conductive layer 10, if provided, is not beconstrued in a limiting sense.

In one preferred and non-limiting embodiment or example, while notwishing to be bound by any particular description, example, or theory,examples of first and second connecting structures 34 and 36 that can beused with the example UBARs 2 shown in FIGS. 1-3 will be described next.

In one preferred and non-limiting embodiment or example, for the purposeof description only, each connecting structure 34 and 36 will bedescribed as having extensions of the various layers and/or substratesforming the various examples resonator bodies 4 shown in FIGS. 1-3.However, this is not to be construed in a limiting sense since it isenvisioned that each connecting structure 34 and 36 can have anysuitable and/or desirable form and/or structure that enable theprovision of one or more separate electrical signals to top conductivelayer 6 and optional bottom conductive layer 10, if provided.

In one preferred and non-limiting embodiment or example, with referenceto FIGS. 5A-5B, which can represent views taken along lines A-A and B-Bin any one or all of FIGS. 1-3, FIG. 5A shows top conductive layer 6 inthe form of comb electrode 27, including back 30 and optional back 32,on top of piezoelectric layer 8. In an example, top conductive layer 6can alternatively be in the form of interdigitated electrode 18. In onepreferred and non-limiting embodiment or example, FIG. 5B shows optionalbottom conductive layer 10 in the form of sheet electrode 33 belowpiezoelectric layer 8 (shown in phantom lines in FIGS. 5B). In anexample, optional bottom conductive layer 10 can alternatively be in theform of interdigitated electrode 18 or comb electrode 27. For thepurpose of the following examples only, top conductive layer 6 andoptional bottom conductive layer 10 will be described as being in theform of comb electrode 18, including back 30 and optional back 32, andsheet electrode 33, respectively. However, this is not to be construedin a limiting sense.

In one preferred and non-limiting embodiment or example, connectingstructures 34 and 36 can include bottom metal layers 40 and 44 (FIG. 5B)in contact with sheet electrode 33 forming optional bottom conductivelayer 10 of resonator body 4. Each bottom layer 40 and 44 can be in theform of a sheet that is covered by piezoelectric layer 8. In an example,each bottom layer 40 and 44 can be an extension of and can be formed atthe same time as sheet electrode 33. In another example, each bottomlayer 40 and 44 can be formed separately from sheet electrode 33 and canbe made from the same or different material as sheet electrode 33. In anexample, connecting structures 34 and 36 can also include top metallayers 42 and 46 on top of piezoelectric layer 8 and in contact withback 30 and back 32, respectively, of comb electrode 27 forming topconductive layer 6 of resonator body 4.

In an example, bottom metal layers 40 and 44 can be connected to contactpads 48 on top surfaces of first and second connecting structures 34 and36 via conductive vias 50 formed in piezoelectric layer 8 that extendbetween said contact pads 48 and bottom metal layers 40 and 44. In anexample, each top metal layer 42 and 46 can have the shape of a sheetthat spaced from the corresponding contact pads 48 by a gap (notnumbered). Each top metal layer 42 and 46 can also include a contact pad58. Each contact pad 48 can be connected, as needed/required, to asuitable signal source (not shown) that can be used to electricaldrive/bias optional bottom conductive layer 10 in any suitable and/ordesirable manner. Similarly, each contact pad 58 can be connected, asneeded/required, to a suitable signal source (not shown) that can beused to drive/bias top conductive layer 6 in any suitable and/ordesirable manner.

As shown by reference numbers 18 and 27 in FIGS. 5A-5B, top conductivelayer 6 can alternatively be in the form of interdigitated electrode 18and optional bottom conductive layer 10 can alternatively be in the formof comb electrode 27 or interdigitated electrode 18.

With reference to FIGS. 6A-6B, which can represent views taken alonglines A-A and B-B in any one or all of FIGS. 1-3, in one preferred andnon-limiting embodiment or example, the examples shown in FIGS. 6A-6Bare similar to the examples shown FIGS. 5A-5B with at least thefollowing exception. Bottom metal layers 40 and 44 can each be in theform a pair of spaced conductors 52 (versus the conductive sheets shownin FIGS. 5A-5B) that are connected to optional bottom conductive layer10 in the form of sheet electrode 33 by a lateral conductor 54 and atether conductor 56. Top metal layers 42 and 46 can each be in the forma conductor 60. Each conductor 60 can be connected to back 30 or back 32of comb electrode 27 forming top conductive layer 6 by a tetherconductor 62. Tether conductor 62 can be vertically aligned with tetherconductor 56 and spaced therefrom by piezoelectric layer 8. In anexample, as shown in FIGS. 6A-6B, the width of tether conductor 62 canbe less than the width of conductor 60 and the width of tether conductor56 can be about the same as the width of tether conductor 62.

With reference to FIGS. 7A-7B, which can represent views taken alonglines A-A and B-B in any one or all of FIGS. 1-3, in one preferred andnon-limiting embodiment or example, the examples shown in FIGS. 7A-7Bare similar to the examples shown in FIGS. 6A-6B with at least thefollowing exception. Some or all of the materials of each connectingstructure 34 and 36 on both sides of the tether conductor(s) 62 and 56,if provided, of said connecting structure can be removed, therebyforming slots that can extend some or all of the distance from the topto the bottom of UBAR 2 on both sides of said tether conductor(s)between the remaining part of said connecting structure and resonatorbody 4. The removal of some or all of the materials of each connectingstructure 34 and 36 on both sides of the tether conductor(s) of saidconnecting structure can, in an example, define a tether structure 76that can include tether conductor(s) 62 and 56, if provided, and theportion of the piezoelectric layer 8in vertical alignment with tetherconductor 62.

With reference to FIG. 7C and with continuing reference to FIGS. 7A-7B,in one preferred and non-limiting embodiment or example, the removal ofsome or all of the materials forming each connecting structure 34 and 36on both sides of the tether conductor(s) 62 and 56, if provided, of saidconnecting structure can be used with any example UB AR 2 shown in FIGS.1-3. For example, FIG. 7C shows a side view of the example UBAR 2 shownin FIG. 1 with the materials of first and second connecting structures34 and 36 on both sides of the tether conductor 62 and 56, if provided,of each said connecting structure removed, as shown in FIGS. 7A-7B. Ascan be understood from FIGS. 7A-7C, the materials removed on both sidesof the tether conductor(s) 62 and 56, if provided, of each connectingstructure can include portions of top conductive layer 6, piezoelectriclayer 8, optional bottom conductive layer 10, if provided, and devicelayer 12, whereupon, in the views shown in FIGS. 7A-7B, no material isvisible in the slots formed by the removal of these materials of eachconnecting structure 34 and 36 on both sides of tether conductor(s) 62and 56, if provided, of said connecting structure. In the example shownin FIGS. 7A-7C, each tether structure 76 can include, from top tobottom, tether conductor 62, a portion of piezoelectric layer 8 invertical alignment with tether conductor 62, optional tether conductor56 (when bottom conductive layer 10 is present), and a portion of devicelayer 12 in vertical alignment with tether conductor 62.

In another example, where a UBAR 2 includes substrate 16 (FIG. 2), shownin phantom in FIG. 7C, and, optionally, one or more additional devicelayers 12-1 and/or substrates 16-1 (FIG. 3), the material formingsubstrate 16 and, if provided, each additional device layer 12-1 and/orsubstrate 16-1 on both sides of the tether conductor(s) 62 and 56, ifprovided, of each connecting structure 34 and 36 can also be removed,whereupon, in the views shown in FIGS. 7A-7B, no material would bevisible in the slots formed by the removal of these materials of eachconnecting structure 34 and 36 on both sides of the tether conductor(s)62 and 56, if provided, of said connecting structure.

In an example, where the views shown in FIGS.7A-7B are of the exampleUBAR 2 shown in FIG. 2, each tether structure 76 can include, from topto bottom, tether conductor 62, a portion of piezoelectric layer 8 invertical alignment with tether conductor 62, optional tether conductor56 (when optional bottom conductive layer 10 is present), a portion ofdevice layer 12 in vertical alignment with tether conductor 62, and aportion of substrate 16 in vertical alignment with the portion of devicelayer 12. In another example, where the views shown in FIGS.7A-7B are ofthe example UBAR 2 shown in FIG. 3, each tether structure 76 caninclude, from top to bottom, tether conductor 62, a portion ofpiezoelectric layer 8 in vertical alignment with tether conductor 62,optional tether conductor 56 (when optional bottom conductive layer 10is present), portions of device layers 12 and 12-1 in vertical alignmentwith tether conductor 62, and portions of substrates 16 and 16-1 invertical alignment with tether conductor 62.

With reference to FIGS. 8A-8B, which can represent views taken alonglines A-A and B-B in any one or all of FIGS. 1-3, in one preferred andnon-limiting embodiment or example, the examples shown in FIGS. 8A-8Bare similar to examples shown in FIGS. 7A-7B with at least the followingexception. Namely, the material forming all or part of at least onedevice layer 12 or 12-1 of each connecting structure 34 and 36 isretained on both sides of the tether conductor(s) 62 and 56, ifprovided, of said connecting structure, whereupon said material of saidat least one device layer 12 or 12-1 is visible in the slots on bothsides of the tether conductor(s) 62 and 56, if provided, of saidconnecting structure. In an example, where the views shown in FIGS.8A-8C are of the example UBAR 2 shown in FIG. 1, each tether structure76 can include, from top to bottom, tether conductor 62, a portion ofpiezoelectric layer 8 in vertical alignment with tether conductor 62,and optional tether conductor 56 (when optional bottom conductive layer10 is present). In this example, device layer 12 is retained and wouldbe visible in the slots shown in FIGS. 8A-8B.

In another example, where the views shown in FIGS. 8A-8B are of theexample UBAR 2 shown in FIG. 2, each tether structure 76 can include,from top to bottom, tether conductor 62, a portion of piezoelectriclayer 8 in vertical alignment with tether conductor 62, optional tetherconductor 56 (when optional bottom conductive layer 10 is present), anda portion of device layer 12 in vertical alignment with tether conductor62. In this example, device layer 12 is retained and would be visible inthe slots shown in FIGS. 8A-8B and substrate 16 (shown in phantom inFIG. 8C) below device layer 12 would also be retained, but would not bevisible in the slots shown in FIGS. 8A-8B.

In another example, where the views shown in FIGS. 8A-8B are of theexample UBAR 2 shown in FIG. 3, each tether structure 76 can include,from top to bottom, tether conductor 62, a portion of piezoelectriclayer 8 in vertical alignment with tether conductor 62, optional tetherconductor 56 (when optional bottom conductive layer 10 is present), anda portion of device layer 12 in vertical alignment with tether conductor62. In an example, where device layer 12 is retained and is visible inthe slots shown in FIGS. 8A-8B, substrate 16 below device layer 12 isalso retained, but would not be visible in the slots shown in FIGS.8A-8B, and each tether structure 76 would also include a portion ofdevice layer 12-1 and a portion of substrate 16-1 in vertical alignmentwith tether conductor 62. In another example, where device layer 12-1 isretained and is visible in the slots shown in FIGS. 8A-8B, substrates 16and 16-1 and device layer 12 would also be retained, but would not bevisible in the slots shown in FIGS. 8A-8B.

In another example shown in FIG. 8D, for the example UBAR 2 shown inFIG. 1 or 2, each tether structure 76 can include, from top to bottom,tether conductor 62, a portion of piezoelectric layer 8 in verticalalignment with tether conductor 62, optional tether conductor 56 (whenoptional bottom conductive layer 10 is present), and a portion of thebody of device layer 12 in vertical alignment with tether conductor 62exposed by the partial removal of device layer 12 on both sides of thetether conductor(s) 62 and 56, if provided, of each connecting structure34 and 36. Where the example shown in FIG. 8D is UBAR 2 shown in FIG. 2,substrate 16 (shown in phantom in FIG. 8D) is retained below devicelayer 12 and would not be visible in the views shown in FIGS. 8A-8B.

In another example, for the example UBAR 2 shown in FIG. 3, each tetherstructure 76 can include, from top to bottom, tether conductor 62, aportion of piezoelectric layer 8 in vertical alignment with tetherconductor 62, optional tether conductor 56 (when optional bottomconductive layer 10 is present), and a portion of the body of devicelayer 12 or device layer 12-1 in vertical alignment with tetherconductor 62 exposed by the partial removal of said device layer 12 or12-1 (similar to the partial removal of device layer 12 shown in FIG.8D) on both sides of the tether conductor(s) 62 and 56, if provided, ofeach connecting structure 34 and 36. In an example, where the portion ofthe body of device layer 12 of UBAR 2 shown in FIG. 3 is removed(similar to the partial removal of device layer 12 shown in FIG. 8D),whereupon the portion of the interior of the material forming devicelayer 12 of UBAR 2 shown in FIG. 3 is visible in the slots shown inFIGS. 8A-8B, each tether structure 76 can also include portions ofdevice layer 12-1 and substrate 16-1 in vertical alignment with tetherconductor 62. In this example, substrate 16 is retained, i.e., noportion of substrate 16 is removed, and would not be visible in theviews shown in FIGS. 8A-8B.

In another example, where the portion of the body of device layer 12-1of UBAR 2 shown in FIG. 3 is removed (similar to the partial removal ofdevice layer 12 shown in FIG. 8D), whereupon the portion of the interiorof the material forming device layer 12-1 is visible in the slots shownin FIGS. 8A-8B, each tether structure 76 can also include a portion ofthe body of device layer 12-1 in vertical alignment with tetherconductor 62. In this example, substrates 16 and 16-1 and device layer12 are retained, i.e., no portions of substrates 16 and 16-1 and devicelayer 12 are removed, and would not be visible in the views shown inFIGS. 8A-8B.

With reference to FIGS. 9A-9B, which can represent views taken alonglines A-A and B-B in any one or all of FIGS. 1-3, for the UBAR 2 shownin FIG. 2, in one preferred and non-limiting embodiment or example, theexamples shown in FIGS. 9A-9B are similar to the examples shown in FIGS.8A-8B with at least the following exception. Each tether structure 76can include a portion of the material forming device layer 12, whereuponin the views shown in FIGS. 9A-9C, portions of substrate 16 can bevisible in the slots formed on both sides of the tether conductor(s) 62and 56, if provided, of each connecting structure 34 and 36. In thisexample, substrate 16 is retained and each tether structure 76 caninclude, from top to bottom, tether conductor 62, a portion ofpiezoelectric layer 8 in vertical alignment with tether conductor 62,optional tether conductor 56 (when optional bottom conductive layer 10is present), and a portion of device layer 12 in vertical alignment withtether conductor 62.

With continuing reference to FIGS. 9A-9B, for the UBAR 2 shown in FIG.3, in one preferred and non-limiting embodiment or example, where devicelayer 12 and substrates 16 and 16-1 are retained, in the views shown inshown in FIGS. 9A-9B, substrate 16-1 can be visible in the slots formedon both sides of the tether conductor(s) 62 and 56, if provided, of eachconnecting structure 34 and 36. In this example, each tether structure76 can include, from top to bottom, tether conductor 62, a portion ofpiezoelectric layer 8 in vertical alignment with tether conductor 62,optional tether conductor 56 (when optional bottom conductive layer 10is present), and a portion of device layer 12-1 in vertical alignmentwith tether conductor 62.

In another example, for the UBAR 2 shown in FIG. 3, where substrate 16is retained, whereupon, in the views shown in FIGS. 9A-9B, substrate 16can be visible in the slots formed on both sides of the tetherconductor(s) 62 and 56, if provided, of each connecting structure 34 and36, each tether structure 76 can include, from top to bottom, tetherconductor 62, a portion of piezoelectric layer 8 in vertical alignmentwith tether conductor 62, optional tether conductor 56 (when optionalbottom conductive layer 10 is present), a portion of device layer 12-1in vertical alignment with tether conductor 62, a portion of substrate16-1 in vertical alignment with tether conductor 62, and a portion ofdevice layer 12 in vertical alignment with tether conductor 62.

In another example shown in FIG. 9D, for the example UBAR 2 shown inFIG. 2, at the interface of substrate 16 and device layer 12, a portionof the material forming the body of substrate 16 can be removedlaterally beneath resonator body 4 and connecting structures 34 and 36,whereupon, as shown in FIG. 9D, bottom portions 64 and 70 of connectingstructures 34 and 36 are exposed, bottom portions 66 and 68 of resonatorbody 4 are exposed, and surfaces 72 and 74 of the body of substrate 16are exposed. In this example, a portion of the material forming the bodyof substrate 16 removed can extend into the plane of FIG. 9D to theportion of the material of substrate 16 vertically aligned with eachtether structure 76. In this example, each tether structure 76 caninclude, from top to bottom, tether conductor 62, a portion ofpiezoelectric layer 8 in vertical alignment with tether conductor 62,optional tether conductor 56 (when optional bottom conductive layer 10is present), a portion of device layer 12 in vertical alignment withtether conductor 62, and a portion of substrate 16 in vertical alignmentwith tether conductor 62 proximate the portion of device layer 12. Inthis example, surfaces 72 and 74 can be visible in the slots shown inFIGS. 9A-9B.

In another, alternative example, for the example UBAR 2 shown in FIG. 3,a portion of the material forming substrate 16-1 or 16 can be removedlaterally beneath resonator body 4 and connecting structures 34 and 36,similar to the removal of the material forming substrate 16 in FIG. 9D,whereupon surfaces (like surfaces 72 and 74) of the material formingsubstrate 16-1 or 16 are exposed and can be visible in the slots shownin FIGS. 9A-9B.

In an example, where the surfaces (like surfaces 72 and 74) of thematerial forming substrate 16-1 of the example UBAR 2 of FIG. 3 areexposed and can be visible in the slots shown in FIGS. 9A-9B, eachtether structure 76 can also include a portion of device layer 12-1 invertical alignment with tether conductor 62 and a portion of materialforming substrate 16-1 in vertical alignment with tether conductor 62proximate device layer 12-1. In this example, only a portion of the bodyof substrate 16-1 is removed to form each slot, and device layer 12 andsubstrate 16 are retained, i.e., no portions of device layer 12 andsubstrate 16 are removed, and are not visible in the views shown inFIGS. 9A-9B.

In another example, where the surfaces (like surfaces 72 and 74) of thematerial forming substrate 16 of the example UBAR 2 of FIG. 3 areexposed and can be visible in the slots shown in FIGS. 9A-9B, eachtether structure 76 can also a portion of device layer 12-1 in verticalalignment with tether conductor 62, a portion substrate 16-1 in verticalalignment with tether conductor 62, a portion device layer 12 invertical alignment with tether conductor 62, and a portion of thematerial forming substrate 16 in vertical alignment with tetherconductor 62 proximate device layer 12. In this example, only a portionof the body of substrate 16 is removed to form each slot.

In one preferred and non-limiting embodiment or example, in any of theexamples discussed above where bottom conductive layer 10 is notpresent, bottom metal layers 40 and 44 of connecting structures 34 and36 need not be present.

In one preferred and non-limiting embodiment or example, each tetherstructure 76 described above can include at least tether conductor 62,optional tether conductor 56 (when optional bottom conductive layer 10is present), and only the portion of piezoelectric layer 8 in verticalalignment with tether conductor 62. In another preferred andnon-limiting embodiment or example, each tether structure 76 can alsoinclude only the portions of one or more of the following in verticalalignment with tether conductor 62: device layer 12, substrate 16,device layer 16-1, and/or substrate 16-1. However, this is not to beconstrued in a limiting sense.

In one preferred and non-limiting embodiment or example, for eachexample resonator body 4 shown in FIGS. 1-3, the widths of at least topconductive layer 6, optional bottom conductive layer 10, if provided,and the portion of piezoelectric layer 8 below top conductive layer 6canall be the same. Also or alternatively, in an example, the widths and/ordimensions of device layer 12, substrate 16, and, if provided, devicelayer 12-1 and/or substrate 16-1, can all be the same as the widthsand/or dimensions of top conductive layer 6, optional bottom conductivelayer 10, if provided, and piezoelectric layer 8.

In one preferred and non-limiting embodiment or example, any one or moreof the surfaces of any example resonator body 4 shown in FIGS. 1-3and/or one or all of the surfaces of anyone or more connectingstructures 34 and/or 36, if provided, can be etched as deemed suitableand/or desirable to optimize the quality factor and/or insertion loss ofany example UBAR 2 shown in FIGS. 1-3. For example, top and bottomsurfaces of any example resonator body 4 shown in FIGS. 1-3 can beetched. Also or alternatively, one or more side surfaces of any exampleresonator body 4 shown in FIGS. 1-3 can be etched, whereupon each ofsaid side surfaces can be vertically planar.

In one preferred and non-limiting embodiment or example, where topconductive layer 6, optional bottom conductive layer 10, if provided, orboth are in the form interdigitated electrode 18, one back 22 or 26 ofsaid interdigitated electrode 18 can be connect to and driven by asuitable signal source while the other back 22 or 26 can be unconnectedto a signal source. In another preferred and non-limiting embodiment orexample, where top conductive layer 6, optional bottom conductive layer10, if provided, or both are in the form interdigitated electrode 18,back 22 of said interdigitated electrode 18 can be connect to and drivenby one signal source and back 26 of said interdigitated electrode 18 canbe connect to and driven by a second signal source. In an example, thesecond signal source can be the same or different than the first signalsource.

In one preferred and non-limiting embodiment or example, each instanceof device layer 12 (or 12-1) can have an acoustic impedance ≥60×10⁶Pa−s/m³. In another example, each instance of device layer 12 (or 12-1)can have an acoustic impedance ≥90×10⁶ Pa−s/m³. In another example, eachinstance of device layer 12 (or 12-1) can have an acoustic impedance≥500×10⁶ Pa−s/m³. In one preferred and non-limiting embodiment orexample, each substrate layer 16 can have an acoustic impedance ≤100×10⁶Pa−s/m³. In another example, each substrate layer 16 can have anacoustic impedance ≤60×10⁶ Pa−s/m³.

In one preferred and non-limiting embodiment or example, the reflectance(R) of an acoustic wave at the interface of device layer 12 andpiezoelectric layer 8 or, if provided, optional bottom conductive layer10, can be greater than 50%. In another example, the reflectance (R) ofan acoustic wave at the interface of device layer 12 device layer 12 andpiezoelectric layer 8 or, if provided, optional bottom conductive layer10, can be greater than 70%. In another example, the reflectance (R) ofan acoustic wave at the interface of device layer 12 and piezoelectriclayer 8 or, if provided, optional bottom conductive layer 10, can begreater than 90%.

In one preferred and non-limiting embodiment or example, the reflectance(R) of an acoustic wave at the interface of a device layer 12 of 12-1and piezoelectric layer 8 or, if provided, optional bottom conductivelayer 10, can be greater than 70%. In an example, the reflectance R atthe interface of any two layers 6 and 8; 8 and 10; 8 or 10 and 12 or12-1; or 12 or 12-1 and 16 or 16-1, or at the interface of a devicelayer 12 or 12-1 and a substrate 16 or 16-1 can be determined accordingto the following equation:

R=|(Zb−Za)/(Za+Zb)|

wherein Za=the acoustic impedance of a first layer, e.g., piezoelectriclayer 8 or, if provided, optional bottom conductive layer 10, that sitsatop of a second layer; and

Zb=the acoustic impedance of the second layer, e.g., device layer 12.

Other examples of first and second layers can include instances ofdevice layer 12 or 12-1 atop of substrate 16 or 16-1.

In one preferred and non-limiting embodiment or example, the overallreflectance (R) of any example resonator body 4 shown in FIGS. 1-3 canbe >90%.

In one preferred and non-limiting embodiment or example, device layer 12can be a layer of diamond formed in a manner known in the art. In anexample, substrate 16 can be formed from silicon.

In one preferred and non-limiting embodiment or example, device layer 12formed of diamond can be grown by chemical vapor deposition (CVD) ofdiamond on a substrate 16 or 16-1 or a sacrificial substrate (notshown). In one preferred and non-limiting embodiment or example,optional bottom conductive layer 10, piezoelectric layer 8, and topconductive layer 6 can be deposited on device layer 12 and, as required,patterned (e.g., comb electrode 27 or interdigitated electrode 18)utilizing conventional semiconductor processing techniques which willnot be described further herein.

Herein, each temperature compensation layer 90, 92, and 94 can compriseat least one of silicon and oxygen. For example, each temperaturecompensation layer can comprise silicon dioxide, or a silicon element,and/or an oxygen element.

In one preferred and non-limiting embodiment or example, each UBAR 2shown in FIGS. 1-3 can have an unloaded quality factor ≥100. In anotherexample, each UBAR 2 shown in FIGS. 1-3 can have an unloaded qualityfactor ≥50. In one preferred and non-limiting embodiment or example, thethickness of piezoelectric layer 8, each device layer 12, and, ifprovided, each substrate 16 of each example resonator body 4 shown inFIGS. 1-3, can be selected in any suitable and/or desirable manner tooptimize the performance of resonator body 4. Similarly, in an example,the dimensions of each example resonator body 4 shown in FIGS. 1-3, canbe selected for target performance such as, without limitation,insertion lost, power handling capability, and thermal dissipation. Inone preferred and non-limiting embodiment or example, when diamond isused as the material for a device layer 12, the surface of said diamondlayer at the interface with bottom layer 12 can be optically finishedand/or physically dense. In an example, the diamond material formingdevice layer 12 can be undoped or doped, e.g., P-type or N-type. Thediamond material can be polycrystalline, nanocrystalline, orultrananocrystalline. In an example, when silicon is used as thematerial for each instance of substrate 16, said silicon can be undopedor doped, e.g., P-type or N-type, and monocrystalline orpolycrystalline. The diamond material forming the device layer can havea Raman half-height-peak-width of ≤20 cm⁻¹.

In one preferred and non-limiting embodiment or example, piezoelectriclayer 8 can be formed of ZnO, AlN, InN, alkali metal or alkali earthmetal niobate, alkali metal or alkali earth metal titanate, alkali metalor alkali earth metal tantalite, GaN, AlGaN, lead zirconate titanate(PZT), polymer or a doped form of any of the foregoing materials.

In one preferred and non-limiting embodiment or example, device layer 12can be formed of any suitable and/or desirable high acoustic impedancematerial. In an example, a material having an acoustic impedance between10⁶ Pa−s/m³ and 630×10⁶ Pa−s/m³ or greater can be considered a highacoustic impedance material. Examples of typical high acoustic impedancematerials can include: diamond (˜630×10⁶ Pa−s/m³); W (˜99.7×10⁶Pa−s/m³); Al; Pt; Pd; Mo; Cr; Ti; Ta; element from Group 3A or 4A of theperiodic table; a transition element from Group 1B, 2B, 3B, 4B, 5B, 6B,7B, or 8B of the periodic table; ceramic; glass, and polymer. This listof high acoustic impedance materials is not to be construed in alimiting sense.

In one preferred and non-limiting embodiment or example, substrate 16can be formed of any suitable and/or desirable low acoustic impedancematerial. In an example, a material having an acoustic impedance between10⁶ Pa−s/m³ and 30×10⁶ Pa−s/m³ can be considered a low acousticimpedance material. Examples of typical low acoustic impedance materialscan include: ceramic; glass, crystals, and minerals having an acousticimpedance between 10⁶ Pa−s/m³ and 30×10⁶ Pa−s/m³; ivory (1.4×10⁶Pa−s/m³); alumina/sapphire (25.5×10⁶ Pa−s/m³); alkali metal K (1.4×10⁶Pa−s/m³); and silicon (19.7×10⁶ Pa−s/m³). This list of low acousticimpedance materials is not to be construed in a limiting sense.

In one preferred and non-limiting embodiment or example, depending onchoice of materials forming each example resonator body 4, one or morematerials typically considered to be high acoustic impedance materialscan function as a low acoustic impedance material of resonator body 4.For example, where diamond is used as the material for device layer 12,W can be used as the material for substrate 16. Hence, achieving adesired reflectance R (discussed above) at an interface of two layers orsubstrates of resonator body 4 can determine which material can be usedas a high acoustic impedance material and which material can be used asa low acoustic impedance material.

In one preferred and non-limiting embodiment or example, a bulk acousticresonator, in accordance with the principles of the present invention,can include a resonator body 4. The resonator body 4 can include apiezoelectric layer 8; a device layer 12; and a top conductive layer 6on the piezoelectric layer 8 opposite the device layer 12. Substantiallyall of a surface of the device layer 12 opposite the piezoelectric layeris for mounting the resonator body 4 to a carrier 14 that is separatefrom the resonator body 4. In the example, it is desirable but notessential that all of the surface of the device layer opposite thepiezoelectric layer can be for mounting the entirety of the resonatorbody to the carrier. In the example, it is desirable but not essentialthat the bulk acoustic resonator can include a connecting structure 34or 36 for conducting a signal to the top conductive layer. In anexample, the device layer can comprise diamond. In an example, the topconductive layer 6 can include a plurality of spaced conductive lines orfingers. In an example, the resonator body 4 can further comprise anoptional bottom conductive layer 10 between the piezoelectric layer 8and the device layer 12.

In one preferred and non-limiting embodiment or example, the resonatorbody 4 can further include a substrate 16 attached to the device layer12 opposite the piezoelectric layer 8. In an example, the surface of thedevice layer 12 can be mounted in its entirety to the substrate 16. Inan example, the surface of the substrate 16 facing the carrier 14 can befor mounting in its entirety directly to the carrier 14.

In one preferred and non-limiting embodiment or example, the surface ofthe device layer 12 facing the carrier 14 can be mounted in its entiretydirectly to the substrate 16. In an example, the surface of the devicelayer 12 facing the carrier 14 is for mounting in its entirety directlyto the carrier 14.

In one preferred and non-limiting embodiment or example, the resonatorbody 4 can further include a second device layer 12-1 between thesubstrate 16 and the piezoelectric layer 8; or a second substrate 16-1between the substrate 16 and the piezoelectric layer 8; or both.

In one preferred and non-limiting embodiment or example, as used herein,“mounting in its entirety” can mean mounting one layer or substratedirectly or indirectly to another layer or substrate. In an example, asused herein, “mounting in its entirety” can, also or alternatively, meanwithout an intentionally introduced space or gap between one layer orsubstrate and another layer or substrate. In another example, as usedherein, “mounting in its entirety” can, also or alternatively, includenaturally occurring spaces that can naturally (but not intentionally)form between one layer or substrate and another layer or substrate.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical preferred and non-limiting embodiments, examples, or aspects,it is to be understood that such detail is solely for that purpose andthat the invention is not limited to the disclosed preferred andnon-limiting embodiments, examples, or aspects, but, on the contrary, isintended to cover modifications and equivalent arrangements that arewithin the spirit and scope of the appended claims. For example, it isto be understood that the present invention contemplates that, to theextent possible, one or more features of any preferred and non-limitingembodiment, example, aspect, or the appended claim can be combined withone or more features of any other preferred and non-limiting embodiment,example, aspect, or the appended claim.

The invention claimed is:
 1. A bulk acoustic resonator comprising: aresonator body including: a piezoelectric layer; a device layer; and atop conductive layer on the piezoelectric layer opposite the devicelayer, wherein substantially all of a surface of the device layeropposite the piezoelectric layer is for mounting the resonator body to acarrier that is separate from the resonator body.
 2. The bulk acousticresonator of claim 1, wherein all of the surface of the device layeropposite the piezoelectric layer is for mounting the entirety of theresonator body to the carrier.
 3. The bulk acoustic resonator of claim1, further comprising a connecting structure for conducting a signal tothe top conductive layer.
 4. The bulk acoustic resonator of claim 1,wherein the device layer comprises diamond.
 5. The bulk acousticresonator of claim 1, wherein the top conductive layer comprises spacedconductive lines or fingers.
 6. The bulk acoustic resonator of claim 1,wherein the resonator body further comprises a bottom conductive layerbetween the piezoelectric layer and the device layer.
 7. The bulkacoustic resonator of claim 1, wherein the surface of the device layerfacing the carrier is for mounting in its entirety directly to thecarrier.
 8. The bulk acoustic resonator of claim 1, wherein theresonator body further comprises at least one temperature compensationlayer positioned: on the top conductive layer opposite the piezoelectriclayer; or between the piezoelectric layer and the device layer.
 9. Thebulk acoustic resonator of claim 1, wherein: the resonator body furthercomprises a substrate attached to the device layer opposite thepiezoelectric layer; the surface of the device layer is mounted in itsentirety to the substrate; and a surface of the substrate facing thecarrier is for mounting the resonator body to the carrier.
 10. The bulkacoustic resonator of claim 9, wherein the surface of the device layerfacing the carrier is mounted in its entirety directly to the substrate.11. The bulk acoustic resonator of claim 9, wherein the substratecomprises silicon.
 12. The bulk acoustic resonator of claim 9, whereinthe resonator body further comprises at least one temperaturecompensation layer positioned: on the top conductive layer opposite thepiezoelectric layer; between the piezoelectric layer and the devicelayer; or between the device layer and the substrate.
 13. The bulkacoustic resonator of claim 9, wherein the resonator body furthercomprises: another device layer between the substrate and thepiezoelectric layer; or another substrate between the substrate and thepiezoelectric layer; or both.
 14. The bulk acoustic resonator of claim1, wherein: the device layer has an acoustic impedance ≥60×10⁶ Pa−s/m³;and the substrate has an acoustic impedance ≤60×10 ⁶ Pa−s/m³.
 15. Thebulk acoustic resonator of claim 1, wherein the resonator body isconfigured to resonate in a composite mode which is a combination ofthickness mode resonance and lateral mode resonance, with the lateralmode resonance being ≥20% of the composite mode resonance.